Duplex film scanning

ABSTRACT

A system for electronically developing an image captured on a film with two or more image capture layers. A developing solution is applied to the film and the film is illuminated by two lights on opposing surfaces. A scanner captures the light reflected from the film by each light source. The two digital images are combined on a pixel-by-pixel basis to form a final image. An alternate embodiment includes a third scanner to capture light transmitted through the film in order to form a third digital scan image which is then combined on a pixel-by-pixel basis with the other two images to form the final image. The invention provides a method for creating an image digitally without first creating an image in the film itself.

This is a continuation of application Ser. No. 07/916,244 filed Jul. 17,1992.

FIELD OF THE INVENTION

This invention generally relates to improvements in image processing andmore particularly to enhancing film processing by applying electronicimaging technology.

BACKGROUND OF THE INVENTION

Image enhancement has been the subject of a large body of patent art.For example, U.S. Pat. No. 4,606,625 discloses a system for colorizingblack and white film in which interpolative techniques are used toreduce the number of frames which have to be individually colorized.

Another example of a prior art image enhancement is U.S. Pat. No.4,907,075 which discloses a method for selecting a limited number ofpresentation colors from a larger palette for a selected image. A threedimensional color histogram of an image is generated and a first coloris selected based upon the color occurring most frequently in the image.Subsequent presentation colors are selected by choosing one at a timethose colors having the highest weighted frequency of occurrence whereinthe weighting is such that colors closest to the previously selectedcolor are weighted very little while colors furthest away from theselected color are weighted the most.

Still another example of an image enhancement system is found in U.S.Pat. No. 4,984,072 which discloses a system and method for colorenhancing an image or a series of images such as a motion picture bydigitally capturing the images, interactively defining maskscorresponding to objects in the images having similar hues, creatingregions from these masks, and for each region, defining a color transferfunction for converting image gray-scale information to unique values ofhue, luminance, and saturation. The gray-scale values within each regionare then processed through that region's color transfer function, andthe resulting colors applied to the image and stored for later retrievaland display.

Still another example of an imaging system is U.S. Pat. No. 5,041,992which discloses a system and method for interactive design of usermanipulable graphic elements. The system allows a user to create andmanipulate graphic elements that can be subsequently employed to createa program.

U.S. Pat. No. 5,041,995 discloses a method for controlling the exposureused to print a developed film negative. The patent pertains toinspection of the negative film medium after the film has beenprocessed.

U.S. Pat. No. 4,554,460 discloses a photodetector automatic adaptivesensitivity system for controlling the exposure of a scanned imageduring the electronic scanning of the object.

None of these prior art patents or any other prior art that applicant isaware of disclose a method or system for enhancing film processingthrough the application of electronic imaging technology.

SUMMARY OF THE INVENTION

Accordingly, it is a primary objective of the present invention toenhance film processing through the application of electronic imagingtechnology.

These and other objectives of the present invention are accomplished bythe operation of a process in the memory of a processor that scans filmwith reflected light from both sides, and by transmitted light, duringthe development of the film. The resulting images are reassembled toproduce a full color image. Only the developer bath is necessary sinceall subsequent processing of the film is performed electronically.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a personal computer system in accordancewith the subject invention; and

FIG. 2a illustrates the relationship of density/signal to noise ratioand exposure time in film in accordance with the subject invention;

FIG. 2b illustrates the relationship of density/signal to noise ratioand exposure time in a specialized film in accordance with the subjectinvention;

FIG. 3 is an illustration of a film developing system in accordance withthe subject invention;

FIG. 4 is a block diagram of a stitching process in accordance with thesubject invention;

FIG. 5A illustrates film stitching in accordance with the subjectinvention;

FIG. 5B illustrates defect elimination in accordance with the subjectinvention;

FIG. 6 is a graph of three basic film dye colors and the range seen by aparticular receptor in accordance with the subject invention;

FIG. 7 is a graph of a layered film and a plot of the six film dyecolors and the range seen by a particular receptor in accordance withthe subject invention;

FIG. 8 is a block diagram of the image processing for film developmentthat resolves each of the pixel values in accordance with the subjectinvention; and

FIG. 9 is an illustration of a duplex film processing system inaccordance with the subject invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is preferably practiced in the context of an operatingsystem resident on an IBM RISC SYSTEM/6000 computer available from IBMCorporation. A representative hardware environment is depicted in FIG.1, which illustrates a typical hardware configuration of a workstationin accordance with the subject invention having a central processingunit 10, such as a conventional microprocessor, and a number of otherunits interconnected via a system bus 12. The workstation shown in FIG.1 includes a Random Access Memory (RAM) 14, Read Only Memory (ROM) 16,an I/O adapter 18 for connecting peripheral devices such as disk units20 to the bus, a user interface adapter 22 for connecting a keyboard 24,a mouse 26, a speaker 28, a microphone 32, and/or other user interfacedevices such as a touch screen device (not shown) to the bus, acommunication adapter 34 for connecting the workstation to a dataprocessing network and a display adapter 36 for connecting the bus to adisplay device 38. The workstation has resident thereon the AIXoperating system and the computer software making up this inventionwhich is included as a toolkit.

POLYSPECTRALLY ENCODED FILM

Polyspectrally encoded film refers to a universal, multispeed colorfilm. The film is used as a recording medium to be scanned and computerprocessed in accordance with the subject invention. The film is notintended to be viewed or printed directly; although, such capability isnot prohibited by the invention. Unlike conventional color film thattypically has over six layers but only three standard dye colors, thisfilm assigns six dye colors among the layers. The processed film isscanned with a separate color for each dye. Although there may becrosstalk between the six dye colors, the scan gives each pixel anequation of six variables. Solving this matrix separates the six dyeimages. The algorithm then selects, for each pixel, the dye image orblend giving the most grainless representation, which enables assemblyof an image superior to current technology films over a wide range ofeffective film speeds.

Conventional photography uses silver halide crystals to "see" light. Asingle photon can excite a sensitizing dye molecule that in turngenerates a single atom of free silver within a crystal. This silveratom returns to the lattice in about a second unless another photoncreates another free silver atom, and the two silver atoms attract eachother to form a stable nucleus that grows as more photons create moresilver atoms. At typically less that ten atoms, the nucleus becomes agate through which developer can reduce all the bound silver in that onecrystal. The film maker chooses the size of the crystals, or grains. Ifthey are large, fewer photons are required per unit area to provide eachgrain the exposure necessary for proper development. However, if thegrains are small, then the image will be "fine-grained", but more lightis necessary per unit area to give each of the tiny grains enoughphotons for development. This is a tradeoff that photographers havestruggled with until the subject invention.

Only about one percent (1%) of the photons actually induce silver atoms,much of the rest are simply passed through the silver halide film. Thus,the film maker has the option of painting several layers of filmtogether, each sensitive as though it were the only layer. However, theemulsion is naturally milky white, and thus light diffuses within thefilm. A high speed film might use a thick emulsion to maximize thechance of trapping each photon. A fine grained film might use a thinemulsion darkened with anti-halation dye to prevent light diffusion andmaximize sharpness at the expense of speed. Using modern thin filmemulsions, seven or more layers can be placed before halation is aproblem.

If all grains were the same size, then they would turn black at the sameexposure resulting in a high contrast image. By mixing different sizedgrains, the film maker can control contrast by letting some big grainsdevelop with very little light and more fine grains develop with morelight. The problem is, the exposure time necessary for the fine grainsto develop over exposes the coarse grains, and looking through thesecoarse grains in the same emulsion damages what could have been finegrained highlights.

The chromogenic monochrome films on the market today sandwich threeemulsions together that develop chromogenically to three colors instandard color developer. This film is identical to color film, exceptthat the three levels have three speeds instead of three colorsensitivities. In the darkroom, the photographer selects the high,medium or low speed emulsion by selecting a red, green or blue filter inthe enlarger. In effect, three pictures are made simultaneously on threefilms, letting the printer select the optimal one. However, theselection is made only on the image as a whole. Thus, one cannot takethe shadows from the high speed film and the white clouds from the lowspeed, fine grained film. Therefore, there is no quality advantage overusing the right conventional film with the right exposure. Thetechnology has two severe limitations. The first is that panchromaticpaper must be used, which precludes the use of variable contrast paperand a bright safelight in the darkroom. The second is that the techniqueis not extendable to color film.

Most color films have far more than three layers. For example, there maybe two magenta forming layers consisting respectively of large and smallgrains. The layer with large grains partially exhausts the couplers whencompletely exposed. Therefore, instead of leaving large sharp grains tomask the highlights as in monochrome film, the layer saturates into amore uniform neutral density by using up dye couplers in that layer. Thefine grained highlights are still damaged as the saturation is notperfect, but less severely than in monochrome film. Color films in facthave lower granularity in highlights than shadows, as opposed to silverimage films which always show an increase along with density.

DIGITAL IMAGE STITCHING

Before extending the technique to color, first consider a techniqueapplicable to standard chromogenic film using computer technology. Usinga scanner and computer processing, monochrome chromogenic film canproduce a superior image to a conventional film by allowing a computerto "stitch" together the shadows from the high speed layer and the neargrainless highlights from the low speed layers. Because the separationof low speed layers from high speed layers is nearly perfect, there isno damage of the highlights by large grains from the shadows. Also, thefilm itself can be improved if prints always come from the computer.Because each layer is only required to reproduce a narrow range ofbrightness, grains outside the narrow range can be eliminated from eachlayer to reduce the granularity and improve the sharpness of theresultant image for a normal exposure range per layer by thinning theemulsion.

FIG. 4 illustrates the "stitching" process diagrammatically. Each pixelis scanned to read the "high" sensitivity and "low" sensitivity layers,giving a high value and a low value for that pixel. Based on these twovalues for each pixel, a ratio is selected that picks the low value whenthe low value is strong, the more noisy high value when the low value isbelow a useable range, and a mix when the low value is weak but stilluseable. Both the high and low values are gamma corrected to linearizeand align their density curves. The ratio selected drives a simple mixerthat outputs the processed levels for the pixel. A more complex methodwould base the "select ratio" block on an average of high and low pixelsover some small region proportional to grain size. This example uses twoemulsion speeds, but the concept works equally well with three or more.

FIG. 5A is an illustration of film development in accordance with thesubject invention. The left column 500 shows the density of pixelsversus exposure, and the right column 510 shows the signal to noise(S/N) 512 or grain to contrast ratio versus exposure. In the raw scandata of the first row 520, the low sensitivity layer requires moreexposure to respond, but gives a better signal to noise ratio.

In the middle row 530, linearization is applied to both the high and lowdata. Linearization, also called "gamma correction", can be performedwith a lookup table that stores the inverse of the film characteristic.Linearization changes both the grain and the contrast in equal amounts,leaving the signal to noise ratio unchanged.

The bottom row 540 mixes the high and low curves. In the region whereboth high and low emulsions are responding, a blending of both imagesgives a signal to noise ratio superior to either individually. The bestweighting ratio for each density is known from statistical mathematicsto be, for the lower layer, the S/N of the low divided by the S/N of thesum of both. For the high layer, the S/N of the high is divided by thesame sum.

POLYSPECTRALLY ENCODED COLOR FILM

The relevancy of this information would diminish if, as in the priorart, the multispeed technology excluded color. Now it will be extendedto color. FIG. 6 is a graph of three basic film dye colors and the rangeseen by a particular receptor in accordance with the subject invention.The shaded area 600 marks the range of color visible by a particularreceptor, such as the green sensitive layer in color paper. Note thatthe width of the dye absorptions and the width of the receptor responsebarely allow the three colors to be placed in the visible spectrumwithout too much crosstalk.

The color names are unimportant. They are based on an old paradigm thatfilms can only modulate in three colors because that is all the humaneye can see, and films are made to be seen. In fact, film can use adifferent color for each of the six or more layers in today's colorfilm. The dyes in a film are picked from a selection that includes peaksat any visible wavelength.

FIG. 7 is a graph of a layered film and a plot of the absorption of dyesin each of the three layers, and the range seen by a particular receptorin accordance with the subject invention. FIG. 7 merges a typical cyandye from transparencies 710, a typical cyan dye from negatives 720, andan intermediate yellow 730 and magenta 740 with standard yellow 740 andmagenta 750 to total six colors. Now the film has twice the informationthat can be seen by the human eye. It is also not usable for printingbecause the overlap of the dyes has made it impossible for anysensitized layer in a paper to respond to just one of the dye layersfree from crosstalk from adjacent dyes.

The film is optimal for a scanning operation. Six scans at differentwavelengths provide six variables for each pixel. Even though there willbe cross talk, these six variables can be solved by six equations forthe six unknowns which are the densities of each dye level for aparticular pixel. Six scans are made at different colors and the matrixis applied to separate the six dye records. For each of the threesensitivity colors, red, green and blue this example yields two dyerecords for the high and low sensitivity levels. The two dye records aremixed using the stitching method as disclosed above to produce anoptimum image. By using this blend of photochemistry and computerscience, a superior film based imaging technique is created.

FIG. 8 is a block diagram of the image processing for film developmentthat resolves each of the six dye densities for each pixel values inaccordance with the subject invention. By operating in the cube rootregression domain, applicant has found superior resolution from a simplelinear regression. The method of this invention changes acceptedconventions. The computer becomes, not an accessory to photography, buta core technology for the photographic process.

ELECTRONIC FILM DEVELOPMENT

Today, a photographer drops off her film at a processing lab and awaitsthe results. The processing lab sends the film to a darkroom forexposure to developer, fix and rinse. Then, the resulting negatives areindividually loaded into an enlarger for creation of positive prints.The invention does away with the processing lab and substitutes acomputer.

For years, photographers have been required to enter a darkroom andcarefully monitor the time that negatives were exposed to the initialchemical mixture. A rare technique was to desensitize the film firstusing a special dye. Then, a safety light could be illuminated and thephotographer can watch the images come alive in the developer. Eachprecious image would get just the right time, some were snatchedquickly, while others had to be nursed for long periods. However, thereis no optimal development time. White clouds may show their lacy detailsbest after only three minutes, but the darkest shadows may not revealtheir secrets for thirty minutes or more, with the resultant destructionof the white clouds. Photographers dreamed of the impossible chemicalfeat of combining the image of the clouds at three minutes with theshadows after thirty minutes. The subject invention turns what couldonly be a dream in the chemical development processing into anelectronic reality.

The invention employs image capture of a developing film multiple timesduring the development process. The scans use a color that does notexpose the film, normally infrared. The timings of the scans give anormal, an extra long and an extra short development.

FIG. 2a illustrates the results on the left with density, and on theright with signal to noise versus exposure. In photography, the signalgain is "contrast" and the noise is "grain." Contrast alone isirrelevant to a digital system because it can be easily changed foraesthetics, so the signal to noise ratios (S/N) 220 and 222 are key.FIG. 2a illustrates that overdevelopment pulls more detail from shadowsbut "blocks up" or "ruins" the highlights, while underdevelopment givessmooth highlights while shadow detail remains latent. It is clear thatif one could develop the film all three ways, then an image could becreated with the best characteristics of each development time.

Building film specifically for this processing allows furtherimprovements. In such a film, the fine grains develop much faster thanthe coarser grains as in FIG. 2b. This order is actually easy to do,usually the problem is to slow down the finer grains so that they do notget ahead of the larger grains. With such a film, the short developmentscan gives a fully developed fine grain image with the signal to noiseratio of a normal fine grained film. Continuing to normal development,the faster fine grains in this special film block up the highlightscompared to a normal film. The block is acceptable, because thehighlights have already been captured in the previous scan. Now anotherscan is performed to capture the middle tones. By constructing a film inthis way, and scanning during development, the wide range, universalnature of a monochrome chromogenic film is realized without the dyes.

Scanning during development seems a messy process. However, there is akey element that obviates much of the apparent messiness. Only thedeveloper bath is necessary. The stop, fix, clear, wash, wetting agent,and dry are all eliminated. This single bath can be stored in pods andapplied as a viscous fluid under a clear cover film with rollers asillustrated in FIG. 3.

ARTIFACT DEFECT CORRECTION

FIG. 5B is an illustration of the physical film medium as it is scannedto create a digital image in accordance with the subject invention.Defects in the film base, such as scratches or variations in theantihalation dye add undesirable artifacts to the image using theprocess as heretofore described. A film 550 is scanned at differenttimes during development to produce an undeveloped image 550 beforecrystals have begun to develop, a partially developed image 560 afterthe fine grains have developed but before the large grains have begun todevelop, and a fully developed image 570 after the large grains haveappeared. All images contain the same defects 553 and scratches 552because they are of the same physical piece of film.

The numerical value representing the light returned from each pixel 562of the partially developed image 560 is divided by that numerical valueof each pixel 554 of the undeveloped image 550 to produce a resultingnumerical pixel value 582. This value is combined with the values of theother pixels to produce a finished image 580. In processed image 580,the film defects 553 and scratches 552 appearing in both the undevelopedfilm image 550 and partially developed film image 560 are cancelled by adivision, leaving only the newly developed grains 586 forming lightinduced shapes 584.

The processing is extended by similarly dividing the pixels of the fullydeveloped image 570 by the pixels of an image 560 made earlier in thedevelopment process to reveal the newly developed large grains 592forming finer light induced shapes 594 free of the film defects 553 andscratches 552, and further, free of interferences from the smallergrains 586 that had already developed in the earlier image 560. Theprocessed images 580 and 590 may be combined using the stitching processdescribed earlier to form a final image with reduced granularity andfree of physical film defects. For simplicity, FIG. 5B shows a caseemploying three scans during development. A larger number can be used toimprove the definition, and the illustrative case of three is notintended as a limitation.

DUPLEX FILM SCANNING

Again, the relevancy of electronic film development would diminish if,as in the prior art, this technology excluded color. The next sectiondiscusses a technique for extending the processing to color. Duplex filmscanning refers to scanning a film with reflected light from both sidesof the film and by transmitted light. The scanning is performed on filmthat is being processed or on film returned to a solution that makes theemulsion opalescent. The system provides a means for developingmonochrome or color film with greatly improved detail, recoveringgreatly improved detail from historical monochrome film, andconstructing a greatly improved color film with no dyes.

For years, the applicant used a process called "inspection development".Panchromatic 4×5 inch negatives were first placed in a desensitizingsolution so that the development could be viewed under a dim safelight.Developing shadow detail emerged from the emulsion side, but from thebase side only the highlight detail emerged. Monochrome films aremanufactured with a high speed layer over a low speed, fine grainedlayer. A stereo microscope reveals the different size of grains atdifferent depths in a finished negative. The opalescence of the unfixedemulsion made it whitish and partially opaque. Backscattering whenviewed from the rear made only the back, fine grained layer of theemulsion visible. However, from the front, only the high speed layer wasvisible. The image could also be viewed by bright, transmitted light tosee all layers together.

On one occasion, applicant accidentally developed a color film using thesame technique. It was a scene of a cityscape at night with manybrightly colored lights. At first, it seemed peculiar that thehighlight/shadow separation applicant was used to observing between thefront and the back had not developed. Then, applicant noticed that somelights were appearing from the front that did not appear from the backand vice-versa. At that point, applicant detected that color film hadaccidentally been used. The red and blue silver images were viewedseparately before any of the colors had formed. It was then thatapplicant realized that if a person could view separated color as thefilm developed, then so could a scanner.

FIG. 9 is an illustration of a duplex film processing system inaccordance with the subject invention. In the figure, separate colorlevels are viewable within a developing film 900 red, 910 green and 920blue. The film is illustrated greatly enlarged. Over a clear film baseare three layers sensitive separately to red, green and blue light.These layers are not physically the colors. Rather, they are sensitiveto these colors. In normal color development, the blue sensitive layerwould eventually develop a yellow dye, the green sensitive layer amagenta dye, and the red sensitive layer a cyan dye.

During development, these layers are opalescent. Dark grains developingin the top layer 920, the blue source layer, are visible from the frontof the film, but are hidden from the rear by the bulk of the opalescentemulsion. Similarly, grains in the bottom layer 900, the red sensitivelayer, are visible from the back by reflected light, but not from thefront. Grains in the middle layer 910, the green sensitive layer, aremostly hidden by reflected light from the front or the back. However,they are visible along with those in the other layers by transmittedlight. By sensing light reflected from the front, the back and lighttransmitted through the film. each pixel in the film yields threemeasured numbers that may be solved for the three colors. The solutioncan use the matrix regression such as that illustrated above in FIG. 8.

Although this technique may be applied to standard color film, anotheroption is a film built specifically for this purpose. The film wouldrequire no color couplers as a color image never develops. Also, theamount of antihalation response to the infrared of the scanner isbalanced so the images are never too dark or too light, and subsequentlydiffused by the emulsion.

The process may be extended to standard black and white films bypracticing the invention to scan the high speed image from the front andthe fine grain highlight image from the back. Following the scanning,the stitching process previously described is applied to recover a moregrain-free image than would be available from a conventionally developedfilm. Similarly, the invention may be extended to historical black andwhite films by returning them to a state of opalescence and scanningfrom the front and back to reveal separately the high speed and lowspeed layers.

All prior art technologies suffer from the presumption that films mustbe printable with an enlarger onto another photochemical receiver suchas paper or directly viewed by a human eye. The invention uses a scannerand processing on a computer to replace the prior art method.

While the invention has been described in terms of a preferredembodiment in a specific system environment, those skilled in the artrecognize that the invention can be practiced, with modification, inother and different hardware and software environments within the spiritand scope of the appended claims.

Having thus described our invention, what we claim as new, and desire tosecure by Letters Patent is:
 1. A system for electronically developingan image captured on a film having two or more image capture layers, thesystem comprising:development means for applying a developing solutionto said film; a first light source for illuminating said film with afirst light; a first scanner for digitally capturing said first lightreflected from said film during development to form a first digital scanimage having a plurality of pixels; a second light source forilluminating said film with a second light, said second light sourceoriented to scan a surface of said film opposite a surface scanned bysaid first light source; and a second scanner for digitally capturingsaid second light reflected from said film during development to form asecond digital scan image having a plurality of pixels; digital imagecombination means for forming a final image by digitally combining apixel from each of said digital scan images to form a final image pixel.2. The system of claim 1, further comprising:a third scanner fordigitally capturing said first or said second light transmitted throughsaid film during development to form a third digital scan image having aplurality of pixels.
 3. The system of claim 2, wherein said digitalimage combination means comprise computer logic means.
 4. The system ofclaim 2, wherein said digital combination means comprises logic meansfor determining three color values for each final image pixel based onsaid scanned image pixel values using cube root regression.